Bottling of beer is generally done at two different scales: very large scale commercial operations (for example, major label beer makers) and very small scale commercial operations (for example, craft breweries).
The bottling of beer using machinery in large scale operations requires enormous amounts of space. A typical commercial bottling machine will have a donut shaped bowl (supply tank) a number of feet across and quite high off of the facility floor. Under the periphery of this large industrial tank a conveyor will carry empty cans to a large number (sometimes over 100) indexing stations, where a large number of fill heads may fill the cans. The speed of production is quite high but the cost of the equipment is also quite high: a million dollars is not uncommon.
Such equipment tends to use one of two filling control methods: there are dosing chamber designs and flow metering designs. In every case, the use of on-off valves to control the flow of the pressurized beer is standard (the beer contains CO2 in solution and thus must be pressurized to maintain flavor). The mechanical designs use some variation on a float valve or ball valve to mechanically stop the flow of beer at the correct moment. An inductive sensor or the like may be used to control the binary (on-off) valve. Volumetric designs use a pre-displaced (similar to being pre-measured) dosing chamber, or time the flow of beer into the can or use a flow meter, etc.
In either case it is absolutely of the first importance to use the equalization of gas pressure during the process. If at any time the pressure is simply chopped off, instantly reduced to ambient air pressure, the CO2 in the beer will burst into bubbles and the beer will foam out of the open-topped can.
A fairly typical volumetric can filler for large scale production may be seen at https://www.khs.com/en/products/single-machines/filling/can/beer/volumetric-filing-system.html?scroll=0.
Widgets in beer cans require even further special handling of pressure. A widget, such as the widgets made by the Ball Company, are small pressure reservoirs actually located within the can. The widget is affixed (usually be food-grade glue) to the dome of the can (the interior bottom). The widget has two very small apertures (½ mm or even less). In production, the can is first pressurized repeatedly with CO2 or N2 to purge out oxygen, which must be removed before bottling of the beer. During this, the CO2 or N2 charges the widget through the apertures. Instructions from the widget maker are to use a pressure cycle which is on-off-on-off (4 seconds-6 seconds-4 seconds-6 seconds) and which consumes a fair amount of time. At certain steps in the process, inverting the can (upside down) may be required. Then when (flat) beer is put into the can at the approximate pressure of the widget gas, the lack of pressure differential and the small size of the apertures prevents the gas from exiting the widget. Thus the beer can is shipped with the gas in the widget charged until the can is opened. The pressure instantly decreases dramatically and the widget instantly uncharges through the small ports, providing the gas into the beer in the can.
Modern craft breweries tend to use a different system, such as that seen at https://www.youtube.com/watch?v=gxFrJzxxR _k. This relatively simple machine is much smaller, more suited to the space available to a microbrewery. It tends to cost in the range of one tenth of a million dollars. However, it may be seen to use a simple gravity feed system and to have only four indexing stations which actually fill beer, thus only four cans are filled simultaneously, which dramatically slows production. It may also be seen to be non-pressurized, as the purging is done by lowering four probes into the four cans at four more indexing stations prior to the four filling stations. An optional seamer may be used after the process to put the top onto the full cans. Production is very slow.
U.S. Pat. No. 5,040,574 (and U.S. Pat. Nos. 5,119,853 and 5,000,234) show a typical mechanically actuated (cam actuated) gas inlet system and outlet system (the “snift” valves). U.S. Pat. No. 5,220,946 is a rather more similar system which does not disclose any details of the valving, in particular, it does not teach toward variable valve control.
U.S. Pat. No. 5,558,135 teaches a CO2 supply valve and a return valve which are both opened and closed to control fill pressure and pressure relief. However, that application states “For decelerating the filling process, the return gas valve can be periodically opened and closed . . . .” Thus this item teaches away from modulating the valve opening. U.S. Pat. No. 6,308,752 teaches that some snifting back through the stem may be possible, and teaches a controller that monitors fluid flow rate and actuates the valves to control purging, filling and gradual venting. Various items which use controllers are known, as is the use of multiple valves (for example, U.S. Pat. No. 66,012,618). U.S. Pat. No. 4,976,295 is one of a type which uses the traditional cam-actuated rotary valves for filling but also incorporates electrical/air operated valves in the vent lines to control filling rate. In these cases the flow rate is controlled for narrow bottle necks and thus it does not apply to canning. In FIG. 3, a valve is shown which may have flow cross-sectional area altered, apparently to vary filling rates into the container. U.S. Pat. Nos. 4,949,764 and 4,360,045 may be similar.